Chord Progression Analyzer
Enter a chord sequence to find a likely key, Roman numerals, scale degrees, and diatonic relationships.
Use spaces, commas, or hyphens between chords. Common symbols such as C, Am, G7, F#m, Bbmaj7, Bdim, Caug, and sus chords are supported.
Chord-by-chord analysis
| Chord | Roman | Degree | Quality | Function | Fit |
|---|
A Chord Progression Analyzer helps you understand how the chords in a progression relate to a musical key. Enter two or more chord symbols, and the tool can estimate a likely major or minor key, convert the progression into Roman numerals, identify scale degrees, show chord quality, and flag chords that may be non-diatonic or altered.
For example, entering C – G – Am – F in C major produces the familiar I – V – vi – IV pattern. Roman numeral analysis is useful because it describes chord relationships independently of one specific key, making progressions easier to study, compare, and transpose.
How to Use the Chord Progression Analyzer
Enter your chords in the progression field. You can write a sequence such as:
C G Am F
The analyzer accepts common major, minor, diminished, augmented, suspended, and seventh chord symbols, including roots with sharps or flats.
Leave the Key setting on Auto Detect Key if you want the tool to estimate the most likely major or minor key. Then select Analyze Progression.
If you already know the key, choose it manually before running the analysis. Manual selection is particularly useful when the same group of chords could reasonably belong to more than one key.
The result shows:
- Likely or manually selected key
- Roman numeral progression
- Scale degree of each chord
- Chord quality
- Basic harmonic function
- Diatonic or non-diatonic status
You can also use Copy Analysis to copy the result or Reset to begin another progression.
If you are trying to discover possible chords rather than analyze an existing sequence, try the Chord Progression Finder.
How Automatic Key Detection Works
Finding a key from chord symbols is not always as simple as looking at the first chord.
The analyzer compares your progression with possible major and minor keys. It considers whether each chord root belongs to the scale, whether its quality matches the expected diatonic chord, and whether important harmonic relationships such as tonic and dominant are present.
For example, the diatonic triads of a major key follow the basic pattern:
I – ii – iii – IV – V – vi – vii°
Uppercase Roman numerals normally represent major-quality chords, while lowercase numerals represent minor-quality chords; diminished quality can be indicated with a degree symbol.
Automatic key detection is still an estimate. A short progression may fit several tonal interpretations, especially when relative major and minor keys share much of the same pitch material.
If you want to identify the key from a finished song rather than entered chord symbols, the Song Key Finder is a more appropriate next step.
Understanding Roman Numeral Progressions
Roman numerals describe the root of each chord relative to the tonic of the selected key.
In C major:
- C is I
- Dm is ii
- Em is iii
- F is IV
- G is V
- Am is vi
- B diminished is vii°
So the progression:
C – Am – F – G
becomes:
I – vi – IV – V
The advantage is portability. If you recognize a progression as I–V–vi–IV, you can rebuild that same harmonic pattern in another key instead of memorizing one fixed set of chord names. Roman numeral notation is widely used for exactly this kind of key-relative analysis and transposition.
If you need to examine the scale itself, the Scale Finder can help you explore the notes associated with a musical scale.
Reading the Chord-by-Chord Analysis
The analysis table gives more detail than the Roman numeral sequence alone.
Chord shows the symbol you entered.
Roman numeral expresses the chord relative to the selected key.
Scale degree identifies the position of the chord root in that key.
Quality identifies the basic chord type, such as major, minor, diminished, augmented, or suspended.
Function gives a simplified harmonic role such as tonic, predominant, or dominant.
Diatonic fit indicates whether the chord’s root and basic quality fit the expected diatonic harmony of the selected key.
These labels are intended as practical guidance rather than a complete classical or jazz harmonic analysis.
If you want to work more directly with individual musical notes, use the Note Finder.
Diatonic vs Non-Diatonic Chords
A diatonic chord is constructed from notes belonging to the key’s underlying scale. A non-diatonic chord introduces one or more notes or chord qualities outside that basic collection.
Non-diatonic does not mean incorrect.
Songs regularly use chromatic chords, borrowed chords, secondary dominants, altered harmonies, and other devices that intentionally move beyond the basic diatonic set. A secondary dominant, for example, temporarily behaves like the dominant of a chord other than the tonic.
The analyzer therefore marks a mismatch as Non-diatonic / altered instead of treating it as an error.
This distinction is useful when studying why a progression contains a chord that sounds effective even though it does not belong naturally to the selected key.
Tonic, Predominant, and Dominant Functions
The analyzer also provides simplified harmonic-function labels.
The tonic function creates a sense of tonal center or stability.
A predominant function commonly helps move the harmony away from tonic and toward dominant territory.
The dominant function often creates tension that points back toward the tonic.
These labels can make a progression easier to understand structurally, but real music is more flexible than a three-category system. Context, chord inversions, melody, rhythm, extensions, chromaticism, and style can all influence how a chord behaves.
Developing your ear alongside theoretical analysis is therefore valuable. The Interval Ear Training tool can help strengthen recognition of pitch relationships.
Why a Progression Can Fit More Than One Key
A progression does not always reveal one unquestionable key.
Consider a short sequence containing C, G, Am, and F. Those chords strongly support C major, but different ordering, emphasis, melody, or phrase endings can influence how the tonal center is perceived.
Relative major and minor keys create another source of ambiguity because they contain the same basic key signature while establishing different tonics.
Chromatic chords can make detection even less certain. A progression may also temporarily tonicize another chord or move between tonal centers.
For this reason, the tool may show an Ambiguous, Moderate match, or Strong match message when Auto Detect Key is used. This describes how clearly one candidate key outranked another in the tool’s comparison; it is not an accuracy percentage.
When you know the intended key, manual selection gives you a more useful Roman numeral analysis.
Chord Analysis in Minor Keys
Minor-key harmony needs extra care.
A basic natural-minor progression can be analyzed using the minor scale, but real tonal music frequently alters the seventh scale degree to produce a stronger dominant chord. That is one reason a major V or V7 chord often appears in a minor key even though it differs from the natural-minor collection.
The analyzer allows for this common dominant relationship, but it should not be treated as a complete analysis engine for every advanced minor-key harmonic convention.
For broader key study, you can also read the site’s guide on how to find the key of a song.
Using Roman Numerals to Transpose a Progression
Roman numerals make transposition much easier because the harmonic pattern remains the same even when the chord names change.
Suppose you have:
C – G – Am – F
in C major:
I – V – vi – IV
To move the same pattern to G major, map those scale degrees onto the G-major chords:
G – D – Em – C
The chord names changed, but the harmonic relationship stayed I – V – vi – IV.
This is useful for songwriting, arranging, changing a progression to suit a singer, or comparing songs written in different keys.
If your workflow eventually involves MIDI note data, the Pitch to MIDI Converter provides another music-analysis tool on the site.
Accuracy and Limitations
The chord-to-scale-degree calculation is straightforward once the key is specified, but automatic key detection can be ambiguous.
Results may require interpretation when a progression contains:
- Only two or three chords
- No clear tonic chord
- Relative major/minor ambiguity
- Modal harmony
- Borrowed chords
- Secondary dominants
- Chromatic chords
- Jazz substitutions
- Frequent modulation
- Complex extended harmony
Automatic Roman numeral analysis is itself an established computational music-analysis problem, which reflects how strongly harmonic interpretation depends on context rather than chord names alone.
The tool is designed for practical chord-progression analysis, not exhaustive classical or jazz harmonic labeling.
Privacy and Browser Processing
The Chord Progression Analyzer processes the chord symbols you enter directly in your browser. The plugin does not require microphone access or an audio upload, and its analysis does not depend on an external music-analysis service.
You can analyze another progression immediately by selecting Reset.
For more browser-based music utilities, explore the full PitchDetector tools collection.
Frequently Asked Questions
What is a chord progression analyzer?
It is a tool that examines a sequence of chord symbols and describes their relationships within a musical key, including Roman numerals and scale degrees.
How do I find the key of a chord progression?
Enter at least two chords and leave the key setting on Auto Detect Key. The analyzer compares the progression with possible major and minor keys and returns its strongest candidate.
What does I–V–vi–IV mean?
The numerals represent chords built on the first, fifth, sixth, and fourth scale degrees of a key. In C major, that progression is C–G–Am–F.
Why does the analyzer say my chord is non-diatonic?
Its root or chord quality does not match the basic diatonic chords expected in the selected key. That does not mean the chord is wrong; it may be borrowed, chromatic, altered, or serving another harmonic purpose.
Can the same chord progression belong to multiple keys?
Yes. Short sequences and relative major/minor relationships can create more than one reasonable tonal interpretation.
Can I choose the key manually?
Yes. Manual key selection is useful when you already know the intended key or disagree with the automatic estimate.
Can the analyzer recognize seventh chords?
The tool recognizes common seventh notation and includes the seventh designation in its practical Roman numeral result.
Does the analyzer detect modulation?
No. It analyzes the progression relative to one selected or estimated key and should not be treated as a complete modulation-detection system.